1. Field of the Invention
The present invention relates in general to solar energy collection, and, more particularly, to cementitious trough structures that collect radiant energy from the sun and methods for making such structures.
2. Description of the Related Art
Photovoltaic (PV) cells have been used to convert solar radiant energy into electricity for many years now. However, despite substantial investment, they have not been widely adopted by the energy industry to generate electricity. There are a couple of reasons for this circumstance.
PV cells are very expensive to create per unit area. Their high cost has made the energy they produce too expensive to compete with conventional sources of energy, such as natural gas and coal.
One way to reduce the area of PV cells needed to produce electricity is to concentrate sunlight onto the cells. If a collector can concentrate sunlight by a factor of 500, then 500 times less area of PV cells is needed to produce the same amount of electricity. Hence, the cost of the energy produced should be vastly reduced.
The idea of concentrating sunlight onto PV cells is not a new one, but the cost and problems associated with building a collector, known in the industry as a solar concentrator, more than offset the cost savings in the reduced number of PV cells. This has prevented PV cells adoption for large-scale electrical energy production.
Many solar concentrators fall into three primary design categories. The first design category is the parabolic dish. This design uses a single parabolic mirror that is similar in shape to a large satellite dish. The mirror collects sunlight and focuses it to a focal point. At this focal point can be PV cells or a heat engine such as a sterling engine.
The second design category is the “power tower.” This design uses many heliostats (small mirrors that track the sun) and points them all to a common focal point. At this focal point can be PV cells or a sterling engine.
The third design is commonly used (albeit in small numbers) in commercial power plant applications and is known in the industry as a solar trough. This design utilizes a single mirror that is parabolic along only one axis that looks something like a trough. This mirror collects sunlight and then focuses this sunlight into a line. At the focus can be a pipe that contains a working substance to be heated, or PV cells. This design has the advantage of a mirror that is easy to manufacture in small size sheets since it is curved in only one direction and it is relatively easy to apply a reflective coating or a glass mirror. Another advantage is the light in the focal plane can form a rectangular shape, important for focusing light onto rectangular PV cells or a continuous pipe structure. The primary drawback to this design is that since sunlight is concentrated only along one axis, a very large mirror is required to achieve high concentrations. Constructing, supporting, and controlling such large mirrors turns out to be a costly endeavor, in fact, too costly to offset the savings produced by needing fewer PV cells.
Because the trough structure establishes and maintains optical alignment of the parabolic mirror or mirror sections, it must be capable of withstanding wind and of securely supporting other solar collector substructures without significantly distorting the mirror shape. Thus, steel trusses anchoring in a concrete foundation is a common trough structure design. However, this and other currently used trough designs are relatively expensive (i.e., they can represent up to 40% of the total solar collector cost), heavy, and cause concerns over longevity and ability to keep mirrors in alignment during periods of high winds.
In view of the problems experienced with the construction and operation of cost-effective solar collectors/concentrators, a need continues to exist for a solar concentrator trough structure that has a minimum of components and has the potential to be less costly to manufacture and maintain while providing a strong supporting structure that better ensures efficient performance of the light collecting surface.